Hybrid memory management

ABSTRACT

Methods and apparatus for managing data storage in hybrid memory devices utilizing single level and multi level memory cells. Logical addresses can be distributed between single level and multilevel memory cells based on a frequency of write operations performed. Initial storage of data corresponding to a logical address in memory can be determined by various methods including initially writing all data to single level memory or initially writing all data to multilevel memory. Other methods permit a host to direct logical address writes to single level or multilevel memory cells based on anticipated usage.

TECHNICAL FIELD

The present disclosure relates generally to memory devices and inparticular the present disclosure relates to managing data stored in amemory device having single and multi level memory cell storagecapability.

BACKGROUND

Memory devices are typically provided as internal, semiconductor,integrated circuits in computers or other electronic devices. There aremany different types of memory including random-access memory (RAM),read only memory (ROM), dynamic random access memory (DRAM), synchronousdynamic random access memory (SDRAM), and flash memory.

Flash memory devices have developed into a popular source ofnon-volatile memory for a wide range of electronic applications. Flashmemory devices typically use a one-transistor memory cell that allowsfor high memory densities, high reliability, and low power consumption.Common uses for flash memory include personal computers, personaldigital assistants (PDAs), digital cameras, and cellular telephones.Program code and system data, such as a basic input/output system(BIOS), are typically stored in flash memory devices for use in personalcomputer systems.

Flash memory typically utilizes one of two basic architectures known asNOR Flash and NAND Flash. The designation is derived from the logic usedto read the devices. In a NAND type flash memory array architecture, thefloating gate memory cells of the memory array are arranged in a matrixof rows and columns. The memory cells of the array are also arrangedtogether in strings, typically of 8, 16, 32, or more each, where thememory cells in the string are connected together in series, source todrain, between a common source line and a column transfer line, oftenreferred to as a bit line. The array is then accessed by a row decoderactivating a row of floating gate memory cells by selecting the wordline connected to their gates. In addition, bit lines can also be drivenhigh or low depending on the current operation being performed.

As the performance and complexity of electronic systems increase, therequirement for additional memory in a system also increases. However,in order to continue to reduce the costs of the system, it is desirableto keep the parts count low. This can be accomplished by increasing thememory density of an integrated circuit by using such technologies asmultilevel cells (MLC). For example, MLC NAND flash memory is a costeffective non-volatile memory.

Multilevel memory cells assign a data state (e.g., as represented by abit pattern) to a specific range of threshold voltages (Vt) stored onthe memory cell. Single level memory cells (SLC) permit the storage of asingle bit of data on each memory cell. Meanwhile, MLC technologypermits the storage of two or more bits per cell (e.g., 2, 4, 8, 16bits), depending on the quantity of threshold voltage ranges assigned tothe cell and the stability of the assigned threshold voltage rangesduring the lifetime operation of the memory cell. The number ofthreshold voltage ranges (e.g., levels), which are sometimes referred toas Vt distribution windows, used to represent a bit pattern comprised ofN-bits is 2^(N). For example, one bit may be represented by two levels,two bits by four levels, three bits by eight levels, etc.

For example, a cell may be assigned a Vt that falls within one of fourdifferent voltage ranges of 200 mV, each being used to represent a datastate corresponding to a bit pattern comprised of two bits. Typically, adead space (which is sometimes referred to as a margin) of 0.2V to 0.4Vis maintained between each range to keep the Vt distributions fromoverlapping. If the voltage stored on the cell is within the first ofthe four Vt distributions, the cell in this case is storing a logical‘11’ state and is typically considered the erased state of the cell. Ifthe voltage is within the second of the four Vt distributions, the cellin this case is storing a logical ‘10’ state. A voltage in the thirddistribution of the four Vt distributions would indicate that the cellin this case is storing a logical ‘00’ state. Finally, a Vt residing inthe fourth Vt distribution indicates that a logical ‘01’ state is storedin the cell.

There are advantages and disadvantages associated with using SLC or MLCmemory. MLC memory is generally considered more cost effective inregards to memory density as MLC memory can, for example, store multiplebits of data in a single memory cell as opposed to SLC memory which isconventionally used to store one bit of data per cell. However,conventional SLC memory can be written to many (e.g., by an ordermagnitude) more times than conventional MLC memory. For example, acharacteristic of conventional MLC memory is that after data has beenerased and re-written about 10,000 times the memory may become subjectto significant read and write errors. Conventional SLC memory on theother hand typically may be erased and re-written about 100,000 timesbefore the reliability of the data begins to deteriorate. These densityand performance characteristics also apply between different types ofMLC arrays. MLC devices with four and eight levels exist today, whiledenser memories are being researched. While an MLC with more levelswould be more efficient (higher density) than an MLC with less levels(lower density), these higher density devices may have performancepenalties over the lower density devices. The case of a device builtwith SLC (two level) and MLC (more than two level) can be generalized asa device with multiple memory arrays, each with its own density andperformance trade-offs. An example is a device built with an array ofMLC (four level) and an array of MLC (eight level). There could even bemore than two arrays of memories, such as SLC, MLC (four level) and MLC(eight level). A common naming convention is to refer to SLC memory asMLC (two level) memory as SLC memory utilizes two levels in order tostore one bit of data as represented by a 0 or a 1, for example. MLCmemory configured to store two bits of data can be represented by MLC(four level), three bits of data by MLC (eight level), etc. An MLC (fourlevel) memory cell is typically referred to as a lower density memorycell than an MLC (eight level) memory due to the lower number of bitsstored per memory cell, for example. SLC (e.g., MLC (two level)) istypically referred to as a lower density memory than MLC (four level)memory and so on.

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art forhybrid memory devices that are adapted to manage the utilization ofmemory of different densities, such as SLC and MLC memory, to takeadvantage of preferred operating characteristics associated with eachtype of memory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a memory module according to anembodiment of the present disclosure.

FIG. 2 is a flow chart illustrating multiple operations according tovarious embodiments of the present disclosure.

FIG. 3 illustrates one storage configuration of a memory deviceaccording to an embodiment of the present disclosure.

FIG. 4 illustrates a move operation of data according to an embodimentof the present disclosure.

FIG. 5 illustrates a write operation of data according to an embodimentof the present disclosure.

FIG. 6 is a functional block diagram of an electronic system having atleast one memory device according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

In the following detailed description of the embodiments, reference ismade to the accompanying drawings that form a part hereof. In thedrawings, like numerals describe substantially similar componentsthroughout the several views. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention. Other embodiments may be utilized and structural, logical,and electrical changes may be made without departing from the scope ofthe present invention. The following detailed description is, therefore,not to be taken in a limiting sense, and the scope of the presentdisclosure is defined only by the appended claims, along with the fullscope of equivalents to which such claims are entitled.

As discussed above, conventional SLC and MLC memory have both positiveand negative attributes associated with them. SLC memory allows forfaster write operations and can withstand far more write operationsbefore reliability of the memory cells begin to degrade as compared toMLC memory. However, SLC memory is not as efficient as MLC memory inthat MLC memory can store multiple bits of data on each memory cellwhereas SLC is used to store only a single bit per cell. Variousembodiments of the present disclosure store data that is frequentlyupdated in SLC memory and store data that is updated less frequently inMLC memory. This can be used to enhance the efficiency and reliabilityof memory devices. Although some embodiments are disclosed withreference to utilizing SLC and MLC memory, the various embodiments arenot so limited. For example, one embodiment may utilize SLC memory,sometimes referred to as MLC (two level) memory, and MLC (four level)memory. Another embodiment may utilize MLC (four level) and MLC (eightlevel) memory. Still other embodiments can utilize three or more memoryarrays such as SLC, MLC (four level) and MLC (eight level) memory in thesame memory device, for example. Other combinations are possibleaccording to the various embodiments of the present disclosure. Thus theembodiments can utilize a combination of different level (e.g., density)memory in a memory device.

Data in a non-volatile memory device can be accessed through anabstraction called a logical block address (LBA) that does not definewhere the data physically resides in the device. The device can alsohave physical block addresses (PBA) that define a physical location, butdoes not define or imply what data is kept in this location. In amagnetic disk device, a physical block address translates to a specificcylinder, head, and sector. In a solid state non-volatile memory device,the physical block address typically refers to a specific memory blockaddress in a specific memory array. Logical block addresses and physicalblock addresses are well known to those skilled in the art. Memorydevices maintain look up tables which map LBAs to their assigned PBAs.Conventional memory devices that have both SLC and MLC memory store datain either SLC memory or MLC memory. The data does not move between theSLC and MLC memory. This is in contrast with various embodiments of thepresent disclosure which cause the data stored in the memory device tomove between SLC and MLC, such as based on the usage (e.g., number ofwrite operations performed) of a given LBA. This usage is determined(e.g., tracked) and maintained for the LBAs of the memory deviceaccording to various embodiments of the present disclosure. Variousembodiments of the present disclosure might also predict the usage for agiven LBA and assign it to SLC or MLC memory accordingly. For examplemany file systems keep a data structure which is used to reference filesto LBAs, such as a File Allocation Table (FAT), LBAs associated withsuch structures are likely to be subject to write operations on everyfile write operation. Thus, LBAs associated with the FAT could initiallybe assigned to SLC memory instead of MLC memory. Other embodimentsadjust the location of a given LBA in SLC or MLC memory by acting inresponse to the actual tracked usage of each LBA. According to someembodiments of the present disclosure, an LBA may move between the SLCand MLC memory based on the actual usage of the LBA during operation ofthe memory device regardless of how the LBA was initially assigned.

FIG. 1 illustrates a memory device according to an embodiment of thepresent disclosure. The memory device in FIG. 1 has been simplified tofocus on various embodiments of the present disclosure. The memorydevice 100 comprises a controller 170 for controlling and managing theoperations of the memory device 100 according to various embodiments ofthe present disclosure including managing the assignment of LBAs toeither SLC or MLC (or between different density MLC) memory. Thecontroller 170 can take the form of discrete logic or a state machine,for example. The controller 170 also incorporates various means forcommunicating with a host, such as a processor 110. For example, thecontroller 170 may incorporate a Universal Serial Bus (USB), SATA, PATA,ATA8-ACS, SD, MMC, Compact Flash, Memory Stick, IEEE 1394 or BA-NANDinterface as are well known in the art. Physical wear leveling of theSLC and MLC memory can also be handled by the controller 170.

The memory device 100 also comprises an array of SLC memory 132 and anarray of MLC memory 134. In some embodiments, the SLC 132 and MLC 134memory may be separate flash memory chips while in others the SLC andMLC memory may be contained on one chip. The memory arrays 132 and 134may also be comprised of different density MLC memory. Array 132 mightbe MLC (four level) and array 134 might be MLC (eight level), forexample. The SLC 132 and MLC 134 memory illustrated in FIG. 1 may eachbe further comprised of multiple banks and blocks of memory. Each of theSLC 132 and MLC 134 memory blocks shown in FIG. 1 can be comprised ofmultiple memory chips. The amount (e.g. capacity) of SLC and MLC memoryof the memory device 100 may or may not be equal. In some embodiments(e.g. a single chip comprising SLC and MLC memory) the size of the SLCarray and MLC array may be assignable depending on the desired amount ofSLC vs. MLC memory for a given application. In another embodimentaccording to the present disclosure, the memory device of FIG. 1 may bea two-way interleaved memory device having two SLC chips and two MLCchips. Other quantities of SLC and MLC chips are also possible accordingto various embodiments of the present disclosure.

The memory device of FIG. 1 also includes a usage table 136. The usagetable is utilized by the controller 170 to store usage data (e.g. writeoperations performed) for the various LBAs of the memory device 100. Forexample, each time a write operation is performed on an LBA, theassociated usage data for that LBA will updated. The usage table 136 mayalso store usage information (e.g., a time stamp) indicating when agiven LBA was last written to as opposed to the number of times it hasbeen written to. For example, LBAs may be mapped based on how much timehas elapsed (e.g., a minute, a day, a month, etc.) since a particularLBA was last written to instead of a cumulative number of times it hasbeen written to. In addition to assigning a time stamp to an LBA, LBAsmay instead be assigned to a time group. LBAs assigned to a first timegroup may represent LBAs used in the current month whereas LBAs assignedto a second time group may represent LBAs used last month, for example.According to various embodiments, usage might also comprise trackingwhich LBAs are utilized at power up of the memory device or during aparticular time frame following power up. The particular time frame mayalso follow a reset operation, for example. These LBAs may then beassigned to lower density (e.g., SLC) memory which can typically beaccessed faster than higher density (e.g., MLC (four level)) memory.This can improve start up performance such as reducing access timeduring a boot load operation, for example. Usage data stored in theusage table 136 is not limited to usage of individual LBAs. Usage datamay also be stored pertaining to use of multiple or ranges of LBAs. Theusage table can also be cleared if desired. For example, a host 110connected to the memory device 100 might send a particular commandinstructing that all or part of the usage table 136 be cleared. Anexample of a usage table is shown in block 136 of FIG. 1.

The usage table 136 may be stored in a standalone component such as anintegrated circuit device having one or both of a volatile andnon-volatile memory portion. For embodiments having both volatile andnon-volatile memory, the volatile memory can maintain the current usagetable during operation of the memory device. The usage table could thenperiodically be copied from the volatile memory to the non-volatilememory. The current usage table 136 can also be loaded into the volatilememory at power up and transferred back to non-volatile memory duringpower down of the memory device. Other embodiments allow for the usagetable 136 data to be stored in the memory array 132/134 of the memorydevice 100. For example, the usage table data may be stored along with(e.g. appended to) the data associated with the LBA in the memorydevice. In other embodiments, the usage table may be stored in adedicated location of either the SLC 132 or MLC 134 memory.

FIG. 1 also illustrates the memory device 100 coupled to a processor110. The memory device 100 is coupled to the processor 110 by way of aninterface 174, which may comprise multiple busses and signals. Forexample, control signals generated by the processor can be coupled tothe memory device by a control bus 172. Additionally, an address bus 142and a data bus 162 are also shown in the figure. The interface 174 mayconform to one of the interface protocols discussed above (e.g. USB,SATA, PATA, et al.).

FIG. 2 illustrates a flow chart of some of the various activitiesperformed by the controller 170 in implementing embodiments of thepresent disclosure. In some embodiments of the present disclosure, thecontroller of the memory device determines where an LBA 200 is to beassigned in the memory device 100. As discussed above, the FAT table islikely to be frequently used. Thus, according to one embodiment of thepresent disclosure, the controller 170 of the memory device 100 mayassign LBAs associated with the FAT to SLC (e.g., MLC (two level) memory214. The FAT LBAs according to this embodiment may also be permanentlyassigned (e.g. ‘pinned’) to SLC memory. In other embodiments, thecontroller may assign the FAT LBAs to MLC memory 206 and the controller170 can move the FAT tables based on usage. Thus, according to oneembodiment, all LBAs may be initially written to MLC memory 206. Inother embodiments, all LBAs may be initially assigned to SLC memory 214.Still other embodiments may assign all LBAs having a write operation tobe performed thereon to SLC memory. In these embodiments, should the LBAcurrently being written to be already assigned to MLC memory, thecontroller 170 can determine if the LBA being written to shouldultimately be assigned to SLC or MLC memory.

The controller also tracks and maintains (e.g., updates) 208/216 theusage table data for LBAs of the memory device during operation. If theusage of an LBA currently assigned to MLC memory exceeds some thresholdvalue 210, the controller will attempt to move the data associated withthe LBA (and reassign the LBA to the location in) to SLC memory 212. Inone embodiment, this threshold value may be 1000 write operationsperformed on a given LBA. The embodiments however are not limited to asingle threshold value. For example, the threshold value may be somefraction of the total write operations performed on the memory 212. Ifthe usage for all the LBAs assigned to MLC memory remain less than thethreshold value, then those LBAs will continue to be assigned to the MLCmemory.

According to one embodiment, each time an LBA is assigned to SLC memory,either from the controller 214 or because an LBA assigned to MLC memoryhas exceeded some threshold value 212, a determination is made regardingwhether a sufficient number of spare locations remain in the SLC memory218. Spare locations are desirable to allow for data handling andhousekeeping functions to be performed on the memory device. Ifsufficient spares will exist in the SLC after the current writeoperation to SLC takes place, no further action by the controller isnecessary and the LBA is assigned to the SLC memory. If however, thecurrent assignment of an LBA to SLC memory will result in too fewremaining spare locations in SLC memory, the controller will performdata management functions according to various embodiments of thepresent disclosure in order to preserve a minimum number of sparelocations in the SLC memory. For example, the controller will review theusage data for each LBA currently assigned to SLC. Whichever LBAcurrently assigned to SLC memory has the least usage associated with it,the data associated with that LBA will be moved to MLC memory 220 (e.g.,the next higher density memory.) In embodiments utilizing a time stampto represent usage for the LBAs, the least recently used LBA assigned toSLC memory would be moved to MLC memory. According to one or moreembodiments, data may be moved to the more dense memory (e.g., from SLCto MLC) if an LBA has not experienced a write operation over aparticular period of time. For example, data may be moved from MLC (fourlevel) to MLC (eight level) memory if the time stamp of thecorresponding LBA indicates that the LBA has not been written to in morethan a month. Other durations are possible according to variousembodiments of the disclosure.

By performing the move operation of the data associated with the leastused LBA currently assigned to SLC memory to MLC memory 220, asufficient amount of spare locations should remain in SLC memory afterthe current LBA write operation to SLC memory is completed. Thecontroller, according to some embodiments may also prevent the writeoperation to SLC memory from proceeding if the usage of the least usedLBA currently assigned to SLC memory exceeds some amount. In thissituation, the LBA prevented from being assigned to SLC memory might beassigned to MLC memory instead. When data associated with an LBA ismoved from SLC to MLC 220, or vice versa 212, the usage data associatedwith that LBA is not incremented, at least according to one embodimentof the present disclosure.

The controller 170 can also perform physical wear leveling operations onthe memory device while the movement of data associated with LBAs eitherwithin or between MLC and SLC memory is occurring according to variousembodiments of the present disclosure. For example, an LBA assigned toMLC memory might be re-assigned to another PBA also located in MLCmemory. Thus, the LBA remains in the desired area of memory (e.g. MLC orSLC) without performing all of the write operations on the same physicalmemory cells of the memory area. Similar physical wear leveling is alsoperformed on the SLC area of memory.

FIGS. 3-5 illustrates a data move and write operation according to anembodiment of the present disclosure. FIG. 3 illustrates a two-wayinterleaved embodiment of a memory device 300. This configuration allowsfor large pieces of data to be shared by two memory chips. However,memory devices according to the present disclosure are not limited totwo-way interleaved configurations. The memory device 300 of FIG. 3 isshown having a controller 302, a SLC memory 306, an MLC memory 308 and adata bus coupling the SLC and MLC memory to the controller 304. In theembodiment shown in FIG. 3, the SLC memory 306 comprises two flash SLCmemory integrated circuits (e.g. chips) 310/312. The MLC memory 308 ofthe memory device 300 shown in FIG. 3 comprises two flash MLC memorychips 314/316. Other embodiments have different numbers of SLC and MLCchips, for example. The memory device shown in FIG. 3 has beensimplified to focus on the embodiments of the present disclosure. Othercomponents may be included in the memory device 300 as are known tothose skilled in the art.

FIG. 3 shows locations 322 in SLC memory 306 along with their assignedLBAs and respective usage data. As discussed with respect to FIG. 1, theusage data may be stored in a location associated with the LBA or may bestored in a different location 136. The embodiment of FIG. 3 illustratesan embodiment wherein four LBAs have been previously assigned to SLCmemory. Other embodiments may only have LBAs assigned to MLC memory atany given time. In the present embodiment shown in FIG. 3, the minimumnumber of spare SLC locations is two. However, embodiments of thepresent disclosure are not limited to maintaining two spare locations.

FIG. 4 illustrates an operation in which an LBA is to be assigned to SLCmemory as is shown in block 214 of FIG. 2. In this example, a moveoperation is performed in order to make room for the new data and so asto maintain the required two spare locations in the SLC memory 306.Again referencing FIG. 2, the data associated with the LBA having thelowest usage is moved 220 to MLC memory in order to maintain the minimumnumber of spare locations in SLC memory 306. In this example, the dataassociated with LBA=2 (having a USAGE=1), which is assigned to location322 is moved 418 to MLC memory 308. FIG. 5 illustrates a write operation520 on LBA=7, wherein the associated data is written to the SLC memory306. The write operation 520 and the move operation 418 may be performedin any order. The embodiments are not so limited that the move operation418 must occur prior to the write operation 520. As illustrated in FIG.5, one of the two required spare memory locations has effectively beenrelocated in the SLC memory. However, upon the conclusion of the writeoperation 520, two required spare locations are shown to still exist inthe SLC memory 306. It should be noted that many more memory locationsand LBAs are possible according to various embodiments of the presentdisclosure than are shown in FIGS. 3-5. In addition, move operationsaccording to various embodiments may also involve moving a number ofLBAs along with the LBA whose usage was used to determine a moveoperation was desired. For example, according to some embodiments, ifany memory segment of the memory has an architecture that is mosteffectively used with accesses of multiples of logical blocks (e.g., 4LBAs, 8 LBAs, etc.), the various embodiments may move groups of LBAs ofthese various sizes even if LBA usage is tracked by single LBAs. Forexample, if it has been determined that LBA=1 is to be moved, LBAs 2, 3,and 4 may also be moved during the same operation according to variousembodiments of the present disclosure.

Referring again to FIG. 1, embodiments according to the presentdisclosure can incorporate a memory device 100 having a standardinterface 174 to couple the memory device with a host, such as processor110. There are various types of standard interfaces such as thoseadapted for hard disk drives (HDDs.) For example, SATA and PATA arecommon HDD interfaces. Additional standard non-HDD specific interfacesalso exist in the art such as USB and SD interfaces. Embodiments of thepresent disclosure employing these and other standard interfaces andprotocols can be used with currently existing processors and controllersalready adapted to utilize these interfaces.

In one embodiment according to the present disclosure, the interface 174and controller 170 are configured to emulate a standard HDD interfaceand protocol. Typically, HDDs contain both cache memory (e.g. RAM) androtating magnetic media. A host interacting with a typical HDD willdecide whether data needs to be stored in the HDD data cache or on themagnetic media. For example, the FAT will often be stored in the HDDdata cache by the host because the FAT is likely to be updatedfrequently. Data that is less likely to be updated is stored on themagnetic media by the host. According to some embodiments of the presentdisclosure, the host 110 is not aware that the memory device 100 is nota typical HDD and therefore utilizes standard HDD commands whencommunicating with the memory device 100. According to embodiments ofthe present disclosure, the controller 170 is configured to receive dataand instructions from the host and direct the storage in SLC 132 and/orMLC 134 memory accordingly. For example, the FAT table that the hostbelieves is being stored in a HDD data cache would instead be stored inSLC memory 132 by the controller 170. Data that the host 110 intends tobe stored on the magnetic media of a HDD (e.g. less frequently updateddata) is stored in MLC memory 134. The controller 170 according tovarious embodiments of the present disclosure can then update the usagetable 136 and perform operations on the LBAs, such as those discussedwith reference to FIG. 2. For example, with respect to decision block210 of FIG. 2, data associated with an LBA assigned to MLC memory 134can be moved to SLC memory 132 (and the LBA re-assigned to thecorresponding location in the SLC) should the usage value for the LBAexceed some particular value.

Another HDD interface and protocol exists which is similar to thestandard HDD interface and protocol described above having RAM cachememory and rotating magnetic media. This interface and protocol isdescribed in the “Non Volatile Cache Command Proposal for ATA8-ACS”which is maintained by the T13 Technical Committee. The ATA8-ACSproposal discusses interfacing with a traditional HDD device havingrotating media and also having non-volatile cache memory instead ofvolatile (e.g., RAM) cache memory as discussed above. The variousembodiments of the present disclosure can also utilize the proposedATA8-ACS protocol. For example, a host 110 may indicate through the useof non-volatile cache commands that data is to be stored in what thehost 110 believes to be the non-volatile cache memory according to theATA8-ACS protocol. A controller 170 according to one or more of thevarious embodiments interprets the ATA8-ACS command and directs the datato the SLC (e.g., lowest density) memory 132 of the memory device 100.Data that the host 110 directs to be stored on what the host 110believes to be the rotating magnetic media would instead be directed bythe controller 170 to the MLC (e.g., higher density) memory 134 of thememory device 100. In accordance with the ATA8-ACS protocol, the host110 may pin one or more LBAs to what the host 110 believes to be thenon-volatile cache memory portion of the memory device. According to thevarious embodiments, these LBAs would be pinned to the SLC memory 132,or the lowest density memory of the memory device 100 according toembodiments of the present disclosure.

In other embodiments of the present disclosure, the host 110 may beaware of the true nature (e.g. flash memory) of the memory device 100.In this embodiment the host can maintain the usage table for the memorydevice and instruct the memory device controller 170 to perform thevarious operations of various embodiments as discussed previously and asshown in FIG. 2. For example, the host 110 can instruct the memorydevice 100 to store data in the SLC memory 132 of the memory devicebased on the nature of the data to be stored. For example, the host 110may assign 214 the FAT for the memory device 100 to be stored in the SLCmemory 132 of the memory device 100 due to the likelihood of frequentupdates to the FAT. The host 110 may also direct data 206 to be storedin the MLC memory of the memory device due to the likelihood that theLBA will not be frequently used (e.g. written to). Along with the datato be stored, the host can also send an indicator (e.g. flag) to thecontroller 170 indicating the intended destination (e.g. SLC or MLC) ofthe data in memory device 100.

According to various embodiments, the host may assign all LBAs to theSLC memory, assign all LBAs to MLC memory or may dynamically decidebased on the nature of the data where a given LBA is to be assigned. Forexample, the nature of the data may refer to the known or anticipatedfrequency of usage of the data to be associated with a given LBA.Whether the LBAs are assigned to SLC, MLC or dynamically assigned, theoperations illustrated in FIG. 2 may be performed on the LBAs accordingto various embodiments of the present disclosure. For example, moveoperations 220 to MLC memory 134 can occur in order to maintain asufficient amount of spare locations 218 in SLC memory 132. The decisionby the host to perform these operations can be made based on usage tabledata as maintained by the host 110. The host 110 can also inquire as tothe amount of SLC and MLC memory contained in the memory device 100.Embodiments of the present disclosure may also utilize memory devicescapable of being configured as entirely SLC, entirely MLC or acombination of both SLC and MLC memory. The host may further inquire asto the separation between SLC and MLC designated memory in devicesconfigured as a combination of SLC and MLC memory.

Additional embodiments allow for the memory device controller 170 or ahost 110 to maintain a pointer directed towards SLC 132 memory insteadof utilizing a usage table 136. Pointers are well known to those skilledin the art. According to these embodiments, a single pointer is usedwhich advances through the SLC 132 memory space. When a new location inSLC memory 132 is needed, the pointer is consulted and the SLC datacurrently in the location referenced by the pointer is then re-mappedand moved to MLC memory 134. The SLC location referenced by the pointeris then overwritten with the new data to be stored in the SLC memory 132and the pointer advances to the next SLC memory 132 location. Theseembodiments may also pin data to SLC (e.g., FAT) that the memory deviceor host deems appropriate to remain in SLC memory.

FIG. 6 is a functional block diagram of an electronic system having atleast one memory device according to an embodiment of the presentdisclosure. The memory device 600 illustrated in FIG. 6 is coupled to aprocessor 610. The processor 610 may be a microprocessor or some othertype of controlling circuitry. The memory device 600 and the processor610 form part of an electronic system 620. The memory device 600 hasbeen simplified to focus on features of the memory device that arehelpful in understanding the embodiments of the present disclosure.

The memory device 600 includes an array of memory cells 630 that can bearranged in banks of rows and columns. The memory array 630 comprises atleast two arrays of memory 632/634 having different densities. Memoryarray segment 632 may be SLC or MLC (four level) memory and memory arraysegment 634 may be MLC (eight level) memory, for example. According toone or more embodiments, these memory cells are flash memory cells. Eacharray 632/634 can consist of multiple banks and blocks of memory cells.

An address buffer circuit 640 is provided to latch address signalsprovided on address input connections A0-Ax 642. Address signals arereceived and decoded by a row decoder 644 and a column decoder 646 toaccess the memory array 630. It will be appreciated by those skilled inthe art, with the benefit of the present description, that the number ofaddress input connections depends on the density and architecture of thememory array 630. That is, the number of addresses increases with bothincreased memory cell counts and increased bank and block counts.

The memory device 600 reads data in the memory array 630 by sensingvoltage or current changes in the memory array columns using sense/datacache circuitry 650. The sense/data cache circuitry 650, in oneembodiment, is coupled to read and latch a row of data from the memoryarray 630. Data input and output buffer circuitry 660 is included forbi-directional data communication over a plurality of data connections662 with the processor 610. Write circuitry 655 is provided to writedata to the memory array 630.

The control circuitry 670 is further shown coupled to a usage tableblock 660. The usage table 660 according to various embodiments of thepresent disclosure stores the data relating to the usage of LBAs of thememory array 630. The usage table block 660 may be a separate memorydevice utilizing both volatile 674 and non-volatile 676 memory as shownin FIG. 6. However, various embodiments of the present disclosure arenot so limited. Other embodiments may utilize the memory array 630 tostore the usage data of the LBAs. The usage data may reside in adedicated location of the memory array 630 or may be stored in alocation corresponding to the LBA in the memory array 630.

Control circuitry 670 is configured in part to implement the features ofvarious embodiments of the present disclosure. In one embodiment, thecontrol circuitry 670 may utilize a state machine. According to one ormore embodiments, the control circuitry 670, address circuitry 640, I/Ocircuitry 660, row decode 644, write/erase 655, column decode 646 andthe sense/data cache 650 functional blocks may comprise the controller170 shown in FIG. 1. Control signals and commands can be sent by theprocessor 610 to the memory device 600 over the command bus 672. Thecommand bus 672 may be a discrete signal or may be comprised of multiplesignals (e.g. command bus). These command signals 672 are used tocontrol the operations on the memory array 630, including data read,data write (program), and erase operations. The command bus 672, addressbus 642 and data bus 662 may all be combined or may be combined in partto form a number of standard interfaces 678. For example, the interface678 between the memory device 600 and the processor 610 may be aUniversal Serial Bus (USB) interface. The interface 678 may also be astandard interface used with many hard disk drives (HDD.) For example,the interface may take the form of an SATA or PATA interface. Other HDDinterfaces are known to those skilled in the art.

CONCLUSION

Various embodiments of the present disclosure provide methods formanaging logical block addresses based on tracked usage of the logicalblock addresses being stored in hybrid memory devices having both SLCand MLC memory. Also disclosed is an apparatus configured to performmultiple logical block address management operations wherein theoperations are performed in response to tracked usage of the logicalblock addresses stored in a hybrid memory device.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement, which is calculated to achieve the same purpose,may be substituted for the specific embodiments shown. This applicationis intended to cover any adaptations or variations of the presentinvention. Therefore, it is manifestly intended that this invention belimited only by the claims and the equivalents thereof.

1. A method for managing data stored on a memory device comprising afirst array of memory cells each memory cell having a first density anda second array of memory cells each memory cell having a second density,comprising: determining usage associated with a logical address of thememory device; at least partially based on the usage, storing dataassociated with the logical address in one of the first array and secondarray of memory cells; and maintaining at least a particular number ofspare locations in the first array of memory cells if locations areavailable in the second array of memory cells by moving data from thefirst array of memory cells to the second array of memory cells.
 2. Themethod of claim 1, wherein the first array of memory cells are singlelevel memory cells (SLC) and the second array of memory cells aremulti-level memory cells (MLC).
 3. The method of claim 1, wherein thefirst array of memory comprises MLC memory cells configured to store afirst number of bits per memory cell and the second array of memorycomprises MLC memory cells configured to store a second number of bitsper memory cell, and wherein the second number is greater than the firstnumber.
 4. The method of claim 1, further comprising storing the usageassociated with logical addresses of the memory device in a usage tableof the memory device.
 5. The method of claim 4, wherein part or all ofthe usage table may be cleared in response to a received command from ahost coupled to the memory device.
 6. The method of claim 4, furthercomprising maintaining the usage associated with the logical addresswherein maintaining the usage associated with the logical addresscomprises updating the usage table in response to a write operationperformed for the logical address.
 7. The method of claim 4, wherein theusage comprises a time stamp corresponding to a most recent occurrenceof a write operation performed for the logical address.
 8. The method ofclaim 4, wherein usage comprises a number of write operations performedfor the logical address.
 9. The method of claim 1, wherein storing datafurther comprises associating a logical address with a physical locationin one of the first memory array and the second memory array in whichthe data is to be stored.
 10. The method of claim 1, wherein determiningusage comprises predicting future usage.
 11. The method of claim 1,further comprising initially storing the data in the second memoryarray.
 12. The method of claim 11, further comprising moving data storedin the second memory array to the first memory array based at least inpart on usage associated with the logical address.
 13. The method ofclaim 1, further comprising initially storing data in the first memoryarray.
 14. The method of claim 1, wherein determining usage comprisesdetermining whether a logical address is accessed during a particulartime period following power up of the memory device.
 15. The method ofclaim 1, further comprising: preventing a write operation to the firstarray of memory cells if a usage of a least used logical addresscurrently assigned to the first array of memory cells exceeds aparticular value.
 16. A non-volatile memory device having physicalstorage locations associated with logical addresses, and wherein thelogical addresses are associated with data, the memory devicecomprising: a first array of memory cells each memory cell having afirst density; a second array of memory cells each memory cell having asecond density; and a controller, wherein the controller is configuredto selectively perform a write operation on the first array of memorycells or on the second array of memory cells and to assign the logicaladdresses to the physical storage locations based at least partially ona number of write operations performed on each logical address, and tore-assign logical addresses to the first array of memory cells if thenumber of write operations exceeds a threshold value and wherein thecontrol circuitry is further configured to maintain at least aparticular number of spare locations in the first array of memory cellsif locations are available in the second array of memory cells by movingdata from the first array of memory cells to the second array of memorycells.
 17. The memory device of claim 16, wherein the control circuitryis further configured to write data to the first array of memory cellsor to the second array of memory cells at least partially in response toa received command from a host coupled to the control circuitry of thememory device.
 18. The memory device of claim 16, wherein the controlcircuitry is further configured to maintain at least the particularnumber of spare locations in the first array of memory cells iflocations are available in the second array of memory cells by movingdata associated with a logical address having a lowest number of writeoperations performed on it to the second array of memory cells or bymoving data associated with a logical address which has not had a writeoperation performed to it for longer than a particular period to thesecond array of memory cells.
 19. The memory device of claim 16, whereinthe control circuitry is further configured to move data associated witha logical address stored in the second array of memory cells to thefirst array of memory cells at least partially in response to the numberof write operations performed on the logical address exceeding athreshold value.
 20. The non-volatile memory device of claim 16, whereinthe controller is further configured to prevent a write operation to thefirst array of memory cells if a usage of a least used logical addresscurrently assigned to the first array of memory cells exceeds aparticular value.
 21. An electronic system comprising: a host thatgenerates memory device control signals; and a memory device, coupled tothe host and configured to receive the memory device control signals,the memory device comprising: a first array of memory cells each memorycell having a first density; a second array of memory cells each memorycell having a second density; and control circuitry, wherein the controlcircuitry is configured to store data in the first array of memory cellsor the second array of memory cells based on interpreting a trackedhistory of received write operations issued to logical addresses of saiddata and wherein the control circuitry is further configured to maintainat least a particular number of spare locations in the first array ofmemory cells if locations are available in the second array of memorycells by moving data from the first array of memory cells to the secondarray of memory cells.
 22. The electronic system of claim 21, whereinthe data is stored in the first array of memory cells or the secondarray of memory cells in response to a command generated by the host andreceived by the memory device.
 23. The electronic system of claim 22,wherein the command generated by the host is generated in response to ananticipated frequency of write operations to be performed on data to bestored in the memory device.
 24. The electronic system of claim 21,wherein the control circuitry is further configured to move datacorresponding to a logical address from the second array of memory cellsto the first array of memory cells in response to exceeding a thresholdnumber of write operations performed on the logical address.
 25. Theelectronic system of claim 21, wherein the control circuitry is furtherconfigured to move data corresponding to a logical address mapped to thefirst array of memory cells and having a least number of writeoperations performed with respect to all logical block addresses mappedto the first array of memory cells to the second array of memory cellsin order to maintain at least the particular number of spare logicaladdress locations in the first array of memory cells.
 26. The electronicsystem of claim 21, wherein the host is configured to perform a bootload operation.
 27. An electronic system comprising: a host thatgenerates memory device control signals; and a memory device, coupled tothe host and configured to receive the memory device control signals,the memory device comprising: a first array of memory cells each memorycell having a first density; a second array of memory cells each memorycell having a second density; and control circuitry, wherein the controlcircuitry is configured to store data in the first array of memory cellsor the second array of memory cells based on interpreting a trackedhistory of received write operations issued to logical addresses of saiddata; wherein the host is configured to perform a boot load operation;and wherein the control circuitry is further configured to store data inthe first array of memory cells or the second array of memory cellsbased at least in part on if the logical address associated with thedata is accessed during the boot load operation.
 28. A memory devicecomprising: a first array of memory cells each memory cell having afirst density; a second array of memory cells each memory cell having asecond density; and control circuitry, wherein the control circuitry isconfigured to determine usage data of a logical address in the memorydevice and store data associated with the logical address in one of thefirst array and second array of memory cells at least partially based onthe usage and wherein the control circuitry is further configured tomaintain at least a particular number of spare locations in the firstarray of memory cells if locations are available in the second array ofmemory cells by moving data from the first array of memory cells to thesecond array of memory cells.
 29. The memory device of claim 28, whereinthe usage data comprises a number of write operations that have beenperformed on the logical address.
 30. The memory device of claim 29,wherein the usage data comprises a time stamp indicating when a mostrecent write operation on the logical address occurred.
 31. The memorydevice of claim 28, wherein the control circuitry is further configuredto perform a wear leveling operation on the first and second array ofmemory cells.
 32. The memory device of claim 28, wherein the usage datacomprises data such that time that has elapsed since a most recent writeoperation was performed on the logical address can be determined fromthe usage data.
 33. A method for managing data stored on a memory devicecomprising a first array of memory cells each memory cell having a firstdensity and a second array of memory cells each memory cell having asecond density greater than the first density, the method comprising:determining whether a logical address is accessed during a particulartime period following power up of the memory device; and storing dataassociated with the logical address in the first array of memory cellsif it is determined that the logical address is accessed during theparticular time period.
 34. The method of claim 33, wherein storing dataassociated with the logical address in the first array of memory cellsif it is determined that the logical address is accessed during theparticular time period comprises storing the data in the first array ofmemory cells, wherein the second density is greater than the firstdensity.
 35. The method of claim 33, further comprising moving datastored in the second memory array to the first memory array based atleast in part on usage associated with the logical address.
 36. Themethod of claim 33, further comprising maintaining at least a particularnumber of spare locations in the first array of memory cells iflocations are available in the second array of memory cells by movingdata from the first array of memory cells to the second array of memorycells.